Fluid flow control device having a throttling element seal

ABSTRACT

A fluid flow control device includes a body defining an inlet, an outlet, and a fluid flow path extending from the inlet to the outlet. A valve seat ring is coupled to the body and defines an orifice through which the fluid flow path passes. A cage is also coupled to the body and defines an interior bore, wherein the cage includes at least one passage through which the fluid flow path passes. A throttling element is sized for insertion into the cage interior bore and movable along an axis between open and closed positions. The throttling element defines a sealing surface oriented substantially parallel to the axis. A seal is positioned to engage the sealing surface when the throttling element is substantially in the closed position, thereby to restrict fluid flow through the valve seat ring orifice.

FIELD OF THE INVENTION

The present disclosure generally relates to fluid flow control devices,and more particularly, to a seal for engaging a throttling element usedin such fluid flow control devices.

BACKGROUND OF THE DISCLOSURE

Fluid flow control devices, such as a control valves and regulators, arecommonly used to control characteristics of a fluid flowing through apipe. A typical device includes a valve body defining an inlet, anoutlet, and a fluid flow path extending between the inlet and theoutlet. A valve seat ring is coupled to the valve body and defines anorifice through which the flow path travels. A throttling element, suchas a plug, is moveable relative to the valve seat ring thereby tocontrol fluid flow through the orifice.

Certain fluid flow control devices employ a cage-style trim in which acage is provided for guiding movement of the throttling element. Thecage defines an interior bore sized to receive the throttling elementand includes at least one passage through which the fluid flow pathpasses. The throttling element is moveable to a closed position in whichthe throttling element closes off at least one passage through the cage.Because of machining tolerances, however, a thin annular gap is presentbetween an exterior surface of the throttling element and the interiorbore surface of the cage. This gap may allow fluid to flow through,thereby creating a potential leak source when the device is intended tobe in the closed position. To fully close the device, a bottom edge ofthe throttling element is typically driven by a closing force suppliedby an actuator into the valve seat ring, thereby to provide a primaryseal in the fluid flow control device.

Conventional primary seals formed by throttling elements pressed againstvalve seat rings are prone to leaks. A primary leak path is formed inthe clearance between throttling element and cage which extends from thecage passage to the valve seat ring orifice. Fluid pressure upstream ofthe primary seal creates a pressure differential across the seal. As aresult, any imperfections in the mating surfaces or other disruptions ofthe seal will allow fluid to leak when the throttling element is in theclosed position. Such leaks may erode the valve seat therebyaccelerating the rate of leakage, which in turn exacerbates seaterosion.

The leakage and erosion problems are even more pronounced when the fluidflow control device is used in an erosive environment. In certainapplications, such as valves used to control the flow of water into aboiler in a power plant, tend to erode the primary seal more quickly.Power plant applications have historically been fairly non-erosive whenthe plant was started only a few times each year and typically operated24 hours a day. More recently, power plants are started on a daily basisand operate only during peak-load daytime hours. As a result, scale thathas built up on the inside of water pipes tends to loosen and break offas the pipes expand and contract during heating up and cooling downperiods each day. These loosened scale particles have a high hardnessand can become entrained in the fluid flow as it passes through the pipeand any fluid flow control devices disposed therein. The velocity ofwater passing through the pipes used to supply the boilers is relativelyhigh, and therefore scale particles entrained in the water impinge onthe primary sealing surfaces and quickly erode the valve seat. Valveseat erosion prevents the valve from shutting off the water flow,reduces power plant efficiency, and causes further damage to the fluidflow control device.

One traditional approach to solving the erosion problem has been to useharder materials for both the seating and the throttling element. Whilethis approach works for certain applications, many power plants haverecently started using chemicals having corrosive properties to treatthe boiler feed water. Frequent cycling operation also makes it moredifficult to control water chemistry. In general, harder materials tendto be more susceptible to corrosion, and therefore this approach may beused only in limited applications.

Another known approach has been to use a soft meal seat on the seat ringwith a hard metal seat on the throttling element. The throttling elementis then pressed against the soft seat ring with sufficient force to makea new seat each time the throttling element closes. Again, this approachworks for limited applications and suffers from several draw backs.First, anything trapped between the seating surfaces as the throttlingelement closes will prevent full shut off, resulting in high velocityfluid flow across the seat which quickly erodes the soft seat material.If the throttling element is somehow able to shut completely, the debriswill create an indentation in the soft seat material. When the valve issubsequently opened and the debris is flushed away, the indentation willcreate a leak path in the seat which again results in high velocityfluid flow and erosion of the seat material when the throttling elementis subsequently closed.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side elevation view, in cross-section, of a fluid flowcontrol device having a seal for preventing fluid flow through a primaryleak path;

FIG. 2 is an enlarged view of a detail of FIG. 1 in cross-section;

FIG. 3 is a side elevation view, in cross-section, of another embodimentof a fluid flow control device having a seal for restricting fluid flowthrough a primary leak path; and

FIG. 4 is an enlarged view of a detail of FIG. 3.

DETAILED DESCRIPTION

A seal for restricting fluid flow through a primary leak path isdisclosed. The seal is disposed in the primary leak path and engages thethrottling element in the closed position to reduce or prevent fluidflow through the leak path. The seal may replace or be provided inaddition to conventional seals formed by the engagement of thethrottling element with the valve seat ring, which are dependent on theactuator force applied to the throttling element. In one embodiment, theseal engages an inner perimeter of the throttling element thereby tolocate the seal away from the normal fluid flow path when the throttlingelement is in the open position.

FIGS. 1 and 2 illustrate a first embodiment of a fluid flow controldevice in the form of a control valve 10 with a seal 12 engaging anouter perimeter of a throttling element 14. The control valve 10includes a valve body 16 defining an inlet 18, an outlet 20, and fluidflow path 22 extending from the inlet to the outlet. A valve seat ring24 is coupled to the valve body 16 and defines an orifice 26 throughwhich the fluid flow path passes. An upper portion of the valve seatring 24 is formed with a contact surface 28.

A cage 30 is coupled to the valve body 16 and engages the valve seatring 24. The cage 30 defines an interior bore 32 and at least onepassage 34 extending through the cage 30 and through which the fluidflow path 22 passes.

The throttling element 14 has an outer surface 36 sized for slidableinsertion into the cage interior bore 32. A stem 38 is coupled to thethrottling element 14 and is further coupled to an actuator (not shown).The actuator reciprocates the stem 38 and attached throttling element 14along an axis 40. The throttling element 14 is shown having a seatingsurface 41 oriented to engage the valve seat ring contact surface 28when the throttling element 14 is in a closed position. The illustratedthrottling element 14 further includes a balancing port 42 forequalizing the fluid pressures acting on opposite sides of thethrottling element 14, as is generally known in the art.

To allow the throttling element 14 to freely move along the axis 40, aclearance gap 44 is provided between the throttling element outersurface 36 and the cage interior bore 32. The gap 44, which isexaggerated in FIG. 2 for clarity, extends around the throttling element14 and therefore is annular in the exemplary embodiment. In a flow downapplication where fluid flows downwardly along the fluid flow path 22 asit passes through the valve seat ring orifice 26, as illustrated inFIGS. 1 and 2, the gap 44 creates two potential leak paths. A first orprimary leak path 46 extends from the cage passages 34 and between thevalve seat ring contact surface 28 and cage seating surface 41 to thevalve seat ring orifice 26. A second or secondary leak path 48 extendsfrom the cage passages 34 and between the cage 30 and throttling element14 towards an upper portion of the throttling element. The throttlingelement 14 is shown having a secondary leak path seal assembly 50 whichslidingly engages the cage interior bore 32 to prevent fluid flowthrough the secondary leak path 48.

The seal 12 is provided to reduce or prevent fluid flow through theprimary leak path 46. The seal 12 is disposed in the primary leak path46 and engages a sealing surface 52, separate from the seating surface41, formed on an exterior perimeter of the throttling element 14. In theillustrated embodiment, the cage 30 and valve seat ring 24 define arecess 54 sized to receive the seal, thereby securing the seal 12 inplace. The throttling element sealing surface 52 is separate from theseating surface 41 and extends substantially parallel to the axis 40.The sealing surface 52 may have an axial width which permits engagementof the seal 12 across a range of throttling element positions as itnears the fully closed position. While the seal 12 is illustrated havinga c-shaped cross-section, it will be understood that other types ofseals may be used. When provided with a C-shaped cross-section asillustrated, the seal 12 may be advantageously energized by fluidpressure present in the gap 44. The seal 52 may be formed of plated orunplated metal, plastic, or other seal materials.

In operation, the seal 12 engages the throttling element sealing surface52 as the throttling element nears the fully closed position. The fluidattempting to travel along the primary leak path 46 is obstructed by theseal 52. Where the seal is formed of a flexible material, the fluid willengage and deform the seal 12 to increase its sealing pressure againstthe throttling element sealing surface 52, thereby further reducingfluid flow along the primary leak path 46. As a result, the seal 12 mayprovide a redundant seal in addition to engagement of the throttlingelement seating surface 41 and valve seat ring contact surface 28.Alternatively, the seal 52 may replace the engagement of the throttlingelement seating surface 41 and valve seat ring contact surface 28 as theprimary seal. In either event, fluid flow along the primary leak path 46is reduced or eliminated, thereby minimizing damage to the valve seatring 24. Additionally, the control valve 10 is no longer reliant onforce provided by the actuator to create a tight seal between thethrottling element 14 and valve seat ring 24, thereby reducingperformance requirements for the actuator.

FIGS. 3 and 4 illustrate an alternative exemplary embodiment of acontrol valve 110 having a seal 112 engaging a throttling element 114 toprovide a primary seal for preventing fluid flow along a primary leakpath 146. The control valve 110 includes a valve body 116 having aninlet 118, and outlet 120, and a fluid flow path 122 extending betweenthe inlet and the outlet. A valve seat ring 124 is coupled to the valvebody 116 and defines an orifice 126 through which the fluid flow path122 passes. The valve seat ring 124 also defines a stop surface 128.

A cage 130 is coupled to the valve seat ring 124 and defines an interiorbore 136. A plurality of passages 134 extends through the cage 130through which the fluid flow path 122 passes.

The throttling element 114 includes an outer surface 132 sized forslidable insertion into the cage interior bore 136. A stem 138 iscoupled to the throttling element 114 and is further coupled to anactuator (not shown) which reciprocates the stem 138 and the throttlingelement 114 along an axis 140 between open and closed positions. Thethrottling element 114 further includes a travel stop surface 141positioned to engage the valve seat ring stop surface 128 thereby tolimit travel of the throttling element 114.

Due to machine tolerances and considerations, a clearance gap 144 isformed between the valve cage interior bore 136 and the throttlingelement outer surface 132. The gap 144, which is exaggerated in FIG. 4for clarity, defines a primary leak path 146 extending from the cagepassages 134 and between the throttling element travel stop surface 141and valve seat ring stop surface 128 to the valve seat ring orifice 126.Accordingly, when the throttling element 114 is in the fully closedposition, fluid may travel from the inlet 118 through the cage passages134, gap 144, and primary leak path 146 to the valve seat ring orifice126.

The seal 112 is provided as a primary seal to reduce or prevent fluidflow along the primary leak path 146. In the illustrated embodiment, thevalve seat ring 124 includes a gland section 156 which defines a channelrecess 158 having an open end oriented outwardly away from the axis 140.The channel recess 158 is sized to receive the seal 112, thereby toretain the seal in place. The throttling element 114 includes a sealingsurface 152 formed on an interior perimeter of the throttling element114 and oriented substantially perpendicular to the axis 140. The seal112 is sized and positioned to sealingly engage the throttling elementsealing surface 152 as the throttling element 114 nears the travel stopdefined by engagement of the stop surfaces 128, 141. The seal 112 isillustrated as an O-ring, however other types of seals made of plasticor formed metal may be used. As with the previous embodiment, thethrottling element sealing surface 152 has an axial width, any pointalong which may sealingly engage with the seal 112.

In operation, the seal 112 advantageously minimizes fluid flow along theprimary leak path 146 and susceptibility to erosion. As the throttlingelement 114 nears the fully closed position, the seal 112 engages theinterior sealing surface 152 of the throttling element, thereby toreduce or prevent fluid flow along the primary leak path 146. Becausethe sealing surface 152 is located on an interior perimeter of thethrottling element 114, it is not directly exposed to the fluid flowpath 122 and therefore is less susceptible to damage from erosiveelements entrained in the fluid. In addition, the seal 112 preventsfluid flow through the primary leak path 146, irrespective of the forcesupplied by the actuator to the throttling element 114. Still further,it will be appreciated that the throttling element travel stop surface141 may erode without degrading performance of the seal 112, since thesealing surface 152 (and not the stop surface 141) forms part of theprimary seal. In that regard, the travel stop surface 141 may beintentionally elongated to increase the life of the throttling element114.

While the embodiments disclosed herein are described as havingparticular inlets and outlets defining a specific flow path, it will beappreciated that the inlet and outlet may be reversed without departingfrom the scope of this disclosure. In particular, rather than the“flow-down” styles illustrated herein, the fluid may flow upwardlythrough the valve seat ring orifice, past the plug, and through the cageto the outlet. The seals disclosed herein would provide the samebenefits noted above in applications having this reverse flow direction.

The foregoing detailed description has been given for clearness ofunderstanding only, and no unnecessary limitations should be understoodtherefrom, as modifications would be obvious to those skilled in theart.

1. A fluid flow control device comprising: a body defining an inlet, anoutlet, and a fluid flow path extending from the inlet to the outlet; avalve seat ring coupled to the body and defining an orifice throughwhich the fluid flow path passes; a cage coupled to the body anddefining an interior bore, the cage including at least one passagethrough which the fluid flow path passes; a throttling element sized forinsertion into the cage interior bore and movable along an axis betweenopen and closed positions, the throttling element defining a sealingsurface oriented substantially parallel to the axis; and a seal beingpositioned immediately adjacent to the valve seat ring to engage thesealing surface when the throttling element is substantially in theclosed position, thereby to restrict fluid flow through the valve seatring orifice; and wherein the seal comprises a C-seal.
 2. The fluid flowcontrol device of claim 1, in which the throttling element sealingsurface has an axial width, and in which the seal engages the sealingsurface at any point along the axial width of the sealing surface.
 3. Afluid flow control device comprising: a body defining an inlet, anoutlet, and a fluid flow path extending from the inlet to the outlet; avalve seat ring coupled to the body and defining an orifice throughwhich the fluid flow path passes; a cage coupled to the body anddefining an interior bore, the cage including at least one passagethrough which the fluid flow path passes; a throttling element sized forinsertion into the cage interior bore and movable along an axis betweena closed position, in which the throttling element engages the valveseat ring, and an open position, the throttling element defining asealing surface located on an exterior perimeter of the throttlingelement and oriented substantially parallel to the axis; and a sealbeing positioned immediately adjacent to the valve seat ring to engagethe sealing surface when the throttling element is substantially in theclosed position, thereby to restrict fluid flow through the valve seatring orifice, and wherein the seal comprises a C-seal.
 4. The fluid flowcontrol device of claim 3, in which the throttling element sealingsurface has an axial width, and in which the seal engages the sealingsurface at any point along the axial width of the sealing surface.
 5. Afluid flow control device comprising: a body defining an inlet, anoutlet, and a fluid flow path extending from the inlet to the outlet; avalve seat ring coupled to the body and having an orifice having a firstdiameter and a seat ring contact surface having a second diametergreater than the first diameter, the flow path extending through theorifice; a cage coupled to the body and the valve seat ring, the cagedefining an interior bore and including at least one passage disposedalong the flow path; a throttling element sized for insertion into theinterior bore of the cage and movable along an axis between an openposition in which the passage through the cage is exposed and a closedposition in which the passage through the cage is closed; the throttlingelement including a seating surface sized to engage the seat ringcontact surface of the valve seat ring when the throttling element is inthe closed position, the throttling element further including anoutwardly facing sealing surface; the cage and the seat ring cooperatingto define a recess; a seal positioned in the recess to engage thesealing surface of the throttling element when the throttling element isin the closed position the cage, the throttling element and the seatring define a primary leak path when the throttling element is in theclosed position, the primary leak path extending between the sealingsurface of the throttling element and the seal, and between the seatring contact surface and the seating surface of the throttling element,wherein the seal is positioned to limit leakage along the primary leakpath; and wherein the seal is a C seal.
 6. The fluid flow control deviceof claim 5, wherein the recess is formed in part by a radially inwardlyfacing portion of the cage.
 7. The fluid flow control device of claim 5,in which the sealing surface is located on an exterior portion of thethrottling element.
 8. A fluid flow control device comprising: a bodydefining an inlet, an outlet, and a fluid flow path extending from theinlet to the outlet; a valve seat ring coupled to the body and having anorifice and a seat ring contact surface, the flow path extending throughthe orifice; a cage coupled to the body and the valve seat ring, thecage defining an interior bore and including at least one passagedisposed along the flow path; a throttling element having an exteriorsurface sized for insertion into the interior bore of the cage andmovable along an axis between an open position in which the passagethrough the cage is exposed and a closed position in which the passagethrough the cage is closed; the throttling element including an inwardlyfacing inner perimeter forming a seating surface sized to engage theseat ring contact surface of the valve seat ring at a point locatedradially outward of the orifice when the throttling element is in theclosed position, the throttling element further including a sealingsurface oriented generally parallel to the axis; a recess formed atleast in part by the seat ring; a seal positioned in the recess toengage the sealing surface when the throttling element is in the closedposition; and wherein a primary leak path is formed between the seal andthe sealing surface of the throttling element when the throttlingelement is in the closed position, and wherein at least a portion of theprimary leak path is disposed radially inwardly of the exterior surfaceof the throttling element and radially outwardly of a diameter of theorifice.
 9. The fluid flow control device of claim 8, wherein the seatring contact surface has a diameter greater than the diameter of theorifice.
 10. The fluid flow control device of claim 8, wherein thesealing surface of the throttling element is formed on a radiallyoutwardly facing portion of the throttling element.
 11. The fluid flowcontrol device of claim 10, wherein the sealing surface of thethrottling element is disposed radially inwardly of the exterior surfaceof the throttling element.